mikb55:
The datasheet says there are optional Wifi cards:
Remote monitoring: VSN300 Wifi Logger Card (opt.), VSN700 Data Logger (opt.)
Wireless local monitoring: VSN300 Wifi Logger Card (opt.)Are these too expensive?
It's absolutely not about the price. It's just there is next to to logging another Rs485 terminal to adjust firmware settings with the ABB Aurora's Manager software (which is remotely not possible with the original wifi card)
Once I get this running, I'd also try to get this 'rs485 over network' via an VPN running. But that is for now a another step ahead. 
Riva:
Any particular reason for wanting ESP8266 modules (apart from cheapness)?
I would normally think of using something like a mesh network with NRF24L01+ modules for a job like this but a quick google shows people have used ESP8266 mesh networks
I asked once for a solution in an Arduino IRC chat for my problem and someone there suggested me ESP8266.
Which benefit do you see in using NRF24L01+?
Thanks for your efforts guys.